A tool for turning or a tool for milling includes a single coated cutting insert or a plurality of coated cutting inserts. As shown in FIG. 1, such a coated cutting insert 1 includes a rake face 2 located on a side carrying chip 6 of a work material 5 in the cutting process and a flank face 3 located on a side opposed to the work material itself. Flank face 3 is structured to continue to rake face 2, with a cutting-edge portion 4 serving as a central point of application for cutting work material 5 lying therebetween.
In order to improve chip ejection performance, in many cases, convex and concave portions called chip breaker 7 are formed in rake face 2 (see FIG. 2). By forming such a chip breaker, the chips produced and separated from the work material are broken into appropriate small pieces, and risk (entanglement with the tool or the work material) due to long chips can be avoided. In addition, as chips at a high temperature due to cutting are immediately ejected, adhesion of the chips to a surface of the tool or to a surface of the work material as well as temperature increase in the surface of the tool can be prevented.
A cutting edge of such a coated cutting insert should be changed when the life of the tool ends. Here, in the case of an insert having a single cutting-edge portion, the insert itself should be changed. Meanwhile, a coated cutting insert having a plurality of cutting-edge portions can be used in such a manner that its orientation is changed several times so as to use its different cutting positions while using an identical datum plane, that is, an unused cutting-edge portion is brought to the cutting position. In some cases, the cutting-edge portion may be attached to another datum plane, where an unused cutting-edge portion may be used.
At a cutting worksite, however, in spite of presence of an unused cutting-edge portion, the coated cutting insert may be replaced, or its orientation may be changed. This is because whether or not the cutting-edge portion has been used is not recognized at the time when the cutting edge is changed or when the orientation of the cutting-edge portion is changed. Therefore, such an operation should be performed only after whether or not the cutting-edge portion has been used is well confirmed.
A coated cutting insert having a flank face and a rake face different in color from each other has been proposed as a method of readily identifying a used cutting-edge portion (Japanese Patent Laying-Open No. 2002-144108 (Patent Document 1)). Specifically, the coated cutting insert is structured such that a wear-resistant base layer called an antifriction coating layer is formed on a substrate and an indicating layer made from a material susceptible to wear is formed on the flank face.
The coated cutting insert structured as above attains an attention-drawing function indicating whether the cutting-edge portion has been used or not, however, the indicating layer formed on the flank face tends to adhere to the work material. Specifically, the indicating layer adheres to the surface of the work material or the work material adheres to the indicating layer, with the result that an uneven cutting edge is used in the cutting process. In such a case, appearance and surface smoothness of the work material after cutting is impaired.
In addition, if the indicating layer is provided on the flank face as in this coated cutting insert, it is difficult to identify which cutting-edge portion has been used when the insert is stored in a storage case or when the insert is placed on a workbench around a machine tool. Usually, the flank face has an area smaller than the rake face, and therefore the insert is stored in the storage case or placed on the workbench with the rake face facing upward, which makes it difficult to observe the flank face.
Patent Document 1: Japanese Patent Laying-Open No. 2002-144108